The invention relates to a method for operating a rechargeable battery cell, in particular a lithium-ion battery cell. The invention also relates to a battery control device.
Electric energy can be stored by means of batteries. Batteries convert chemical reaction energy into electric energy. Primary batteries and secondary batteries are differentiated here. Primary batteries are only functional once, whereas secondary batteries, which are also referred to as accumulators, can be recharged. A battery thereby comprises one or a plurality of battery cells.
Particularly so-called lithium-ion battery cells are used in an accumulator. These are characterized inter alia by high energy densities, thermal stability and an extremely low self-discharge. Lithium-ion batteries are used inter alia in motor vehicles, particularly in electric vehicles (EV), hybrid vehicles (hybrid electric vehicle, HEV) as well as in plug-in hybrid vehicles (plug-in hybrid electric vehicle, PHEV).
Lithium-ion battery cells have a positive electrode, which is also referred to as cathode, and a negative electrode, which is also referred to as anode. The cathode and the anode each comprise a current collector, to which an active material is applied. An active material for the cathode relates, for example, to a metal oxide. The active material for the anode relates, for example, to silicon; however, graphite is also widely used as the active material for anodes.
Lithium atoms are embedded in the active material of the anode. During operation of the battery cell, i.e. during a discharge process, electrons flow in an external circuit from the anode to the cathode. During a discharge process, lithium ions travel within the battery cell from the anode to the cathode. In so doing, the lithium ions are reversibly deintercalated from the active material of the anode, which is also referred to as delithiation. During a charging process of the battery cell, the lithium ions travel from the cathode to the anode. In so doing, the lithium ions again reversibly intercalate into the active material of the anode, which is also referred to as lithiation.
The electrodes of the battery cell are designed in a foil-like manner and are wound with interposition of a separator, which separates the anode from the cathode, to an electrode winding. Such an electrode winding is also referred to as jelly roll. The electrodes can also be superposed to form an electrode stack.
The two electrodes of the electrode winding or the electrode stack are connected electrically to poles of the battery cell, which are also referred to as terminals, by means of collectors. A battery cell generally comprises one or a plurality of electrode windings or the electrode stack. The electrodes and the separator are usually surrounded by a liquid electrolyte. The electrolyte is conductive for the lithium ions and enables the transport of the lithium ions between the electrodes.
By construction, each battery cell has a limit voltage. Slightly exceeding the limit voltage during a charging process can lead to a faster ageing of the battery cell. Strongly exceeding the limit voltage during a charging process can lead to the battery cell overheating in combination with a fire or an explosion.
A method for charging as well as equalizing of chargeable battery modules is, for example, known from the German patent application DE 10 2013 204 346 A1.
A method for operating, particularly charging and discharging a chargeable battery in a vehicle is disclosed in the Japanese patent application JP 2012-2000048 A.
A method for operating battery cells, in particular for charging battery cells by means of recuperation, in a vehicle is known from the WIPO patent application WO 2014/057802.